The polarizing element utilized in display devices is formed of a composite film structure of for example an iodine-dyed polyvinyl alcohol (PVA) film and a protective film for protecting this film, for example, a triacetyl cellulose (TAC) film.
Recently, development of a new concept thin-film polymeric polarizing film being formed by a simple coating process has been sought as an alternative to the film type multi-layer element through the iodine dyeing. The process technology of thin-film formation of the polarizing film through such a structure simplification and low-cost manufacturing is a key technology for LCD cost saving and flexible display embodiment, where the technology for preparing the polarizing element by coating a dye layer comprising a dichroic dye and a polymeric liquid crystal compound as in Patent Document 1 (JP Unexamined Patent Publication No. 2010-152351) has been known.
However, to use the polarizing element in the display devices, physical properties are required, which can maintain the absorption spectrum even under severe conditions such as high temperature conditions, but since the coating type polarizing element with the dichroic dye has the lowered heat-resistant stability, there is a problem that the dye molecules are degraded in high temperature conditions to change the absorption spectrum, whereby there is a limit in using it for the display device. Therefore, recently, it is a trend in the display device field to increase studies for developing the coating type polarizing element that can ensure the heat-resistant stability.